Electrical synchronization generator



Dec. 26, 1939. K SCHLESINGER 2,185,136

ELECTRICAL SYNCHRONIZATION GENERATOR Filed June 11, 1937 3 Sheets-Sheet l hue/710w Dec. 26, 1939. K. SCHLESINGER 2,185,136

- ELECTRICAL SYNCHRONIZATION GENERATOR iled June 11, 1937 5 Shee'tsSheet 2 Dec. 26, 1939. sc s 2,185,136

ELECTRICAL SYNCHRONI ZATION GENERATOR Filed June ll, 1937 3 Sheets-Sheet 3 Patented Dec. 26, 1939 PATENT OFFICE ELECTRICAL SYNCHRONIZATION GENERATOR Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio,

Inc., a

.. corporation of New York Application June 11, 1937, Serial No. 147,800 In Germany June 13, 1936 4 Claims.

For the generation of the impulses necessary for television synchronization purposes in transmitters using scanning cathode Jrays it is known to utilize the mains frequency as basic frequency and to derive the synchronizing impulses from the same by frequency multiplication. Synchronization generators of this nature have the advantage that the ratio between line frequency and image change frequency is absolutely constant and that the number of lines per image, therefore, always remain the same even if the mains frequency is subject to considerable vari ations. A disadvantage of these generators consists in the fact that in the frequency multiplier the maximum frequency is merely impulsed in groups by the preceding lower frequency. Upon a multiplication of mi only each nth oscillation is impulsed, whilst the following n--1 oscillations oscillate with the free frequency of the concerned overtone generator. If now the primary frequency differs from the free frequency by an amount which depends on the irregularity of the mains frequency, the line frequency is no longer isochronous. This causes that straight vertical lines of the original image are reproduced in the form of broken lines. The only way out of this difliculty consists in producing the line frequency by an oscillator, on which no external impulses are acting, but which is corrected only by a D. C. potential at a speed slow as compared with the image-change frequency.

It is an object of the invention to supply the correcting potential to this generator by means of circuits having a time constant greater than the image-change period in order to avoid too quick changes of the oscillator period.

Another object of the invention is to provide an oscillator the frequency of which is reduced from the line frequency (or a higher frequency) in 3 to 5- stages to the mains frequency, to compare its frequency with the actual mains frequency by means of a special tube connection, and to obtain this way a current depending on the phase difference of both frequencies and to use this current for tuning the generator of the highest frequency.

Further objects of the invention are described in the following specification.

In the drawings Fig. 1 shows the connections of the frequency transformers and the impulse generators.

Figs. 2 and 4 and 5 are connections of frequency (or phase) comparators and correctors, whilst Figs. 3 and 3a are diagrams of oscillations.

Figs. 4 and 5 show further embodiments of the invention.

In Fig. 1, I is a back-coupled three-pole tube the oscillatory circuit of which consists of a condenser 2 and a coi13. Its natural frequency is a little higher than the corresponding multiple of the mains frequency and is equal to twice the line frequency (order of magnitude approximately 20,000 periods). Between the oscillatory circuit and the oscillator there are located both at the grid as well as the anode series resistances l and 5. These serve to limit the currents traversing the tube and make the frequency to a large extent independent of the properties of the tube. Variations in the anode potential are to a large extent precluded by automatic grid bias generation at the resistance 6. In a tube-having at least two grids, preferably in a pentode or mixing hexode I, there occurs a first frequency reduction to one-half. For this purpose an oscillatory circuit 8/9 is tuned to half the frequency of the circuit 2 3 and used for back-coupling anode and first grid of tube 1. Braking resistances l0 and II are serially connected to grid and anode. These braking resistances have approximately 10 ohms respectively 10 ohms. By means of the intercepting grid l3 which is connected with the oscillation grid of the generator I the frequency reduction is performed in a well known manner.-

The next frequency reducing stage which is typical for the following stages of the cascade, consists of a pentode IS with automatic generation of the grid bias at a resistance 6. The oscillation is produced in reaction coupling between the anode and the first grid l6 of the pentode by means of an oscillatory circuit 20/62. The intercepting grid I3 is connected to the cathode by means of a resistance IS. The synchronization and frequency reduction is performed by connecting the intercepting grid l3 to the anode of the preceding stage I by means of a large condenser I 8 and a resistance IT. The latter should exceed the impedance of the anode circuit of the generator I and is provided in order to avoid an interfering of the oscillations. It is possible by the stated connection to perform a frequency reduction up to 9:1, even when the synchronizing oscillation differs up or down by 'a. few per cent. The next stage is conducted in exactly similar fashion from the anode of the five pole tube 15 by way of a blocking condenser l8, which must have an n-times greater capacity than the blocking condenser |8-'-corresponding to the reduced frequency, and a series resistance II to the intercepting grid of the next reducer pentode.

It has been found that it is possible in a cascade of frequency reducers of the described kind, to obtain a frequency correction of all stages together by correcting the highest frequency only. A condition for this possibility consists in an exact tuning of the intermediate stages. In the stages of lower frequency having unvariable condensers and iron-core coils the fine tuning is made by means of resistances |4 connected in series to the coils, the maximum value of which is not so great that the oscillation ceases. The resistances M are of the order of 200 to 500 ohms and have the effect that if they are increased the frequency of the circuit is somewhat reduced.

Fig. 2 shows a method of comparing the lowest frequency with the mains frequency and of utilizing the stated phase difierence for correcting by means of a tube having two seriesly arranged control grids, which. are conveniently separated by a screening grid, i. e., preferably by a fivepole tube 2|. Both control grids, viz. the inner grid 22 and the third grid 23, are so biased that they just interrupt the electronic current in their control space. These biases are produced by two resistances 24 and 25 and passed to the grids by grid leaks 26 and 21. If there are conducted to these two grids, for example by way of condensers 28 and 29, two alternating potentials from the generators 30 and 3| the anode current disappears completely when the two generators accidentally have the same frequency and oscillate in phase opposition. In all other cases, for example also in the case of small phase differences in generators of equal frequency, anode current impulses arise.

The conditions are depicted in Fig. 3. 30 is the grid alternatingpotential belonging to the generator 30 in Fig. 2, shown positively upwards. In similar fashion 3|a is a grid alternating potential of the same frequency but exactly opposite phase, which is conducted from the mains 3| to the intercepting grid 23 by means of a condenser 29. If this oscillation has a somewhat higher frequency than 30, the same has the disposal of the curve 3|b; if it has a lower frequency, it has the disposal of the curve 3|c. It is to be recognised now that in the first case there arises between the points of time a and b an anode current impulse 32. During all other times the anode current is suppressed. It is, however, equally as clear that a lagging frequency of the mains according to 3|c is unable to produce an anode current at all, at least during its first period, but at the most only after expiry of a plurality of beat cycles. Accordingly the case of 3|b only is realised by tuning the generator 30 in Fig. 2 to a frequency lower than that of the mains. The amplitude of the anode current impulse increases with the phase error. It charges a condenser 33 shunted by a leak resistance 36. The D. C. potential obtained on this condenser is smoothed by a filter 35a/35b the time constant of which, as mentioned above, is greater than an image-change period, i. e. approximately of a second in the case of 25 images per second. Prac+ tically 33 and 35b have 0.5 mf., 35a and 36 0.1

megohm. I

The frequency correcting tube 34 operates as resistance amplifier with an anode resistance 31 which is greater than the oscillation resistance of the circuit to be detuned. The latter is the is equal to zero.

it is connected by the lead II. There may be employed any of the known connections in selftuning radio receivers. The connection according to Fig. 2 has been found to be particularly suitable. The detuning condenser 38 of approximately 0.001 mf. acts as more as a shunt to the condenser 3 the greater the anode current and accordingly the conductivity of the tube. 34 may be. Normally, if the two oscillation frequencies 30/3| coincide, the anode current of the tube 2| vides maximum emission, and the circuit 2/3 is detuned to lowest frequency.

According to an additional feature of the invention, a correction may also be performed towards both sides, so that it is possible to vary. the circuit 2/3 to higher and to lower frequencies.

In Fig. 3a the mutual phase of the potentials 30 and 3 a shown in Fig. 3 is reversed, so that the generator potential 30 is negative, whilst the mains potential 3| in exact opposition thereto is disposed in positive. Consequently anode current will not be able to flow upon advance of the mains phase according to'3lb during the first period in a tube, to the inner grid of which there is applied the potential 30 and to the outer grid of which the.potential 3|. On the other hand, upon a lagging of the mains phase according to curve 3|c an anode current will flow in this case in the time interval a b, which current re- In this case the tube 34 prosults in the impulse designated 32'. A frequency correction is accordingly possible towards both sides, if there are employed for frequency comparison two tubes operating in push-pull of which the one generates the impulses 32 and the other the impulses 32.

A suitable circuit connectionis illustrated in Fig. 5. In the same 2| and 2| are the two pentodes serving for frequency comparison, the inner grids 22 and 22' of which are connected to the generator 30, the outer grids 23 and 23' to the mains 3| in phase opposition. Impulses then result in the anode circuit of the tube 2| upon an advancing phase of the mains 3|, whilst in the case of retardation impulses occur in the anode circuit of the tube 2|. These impulses, exactly in the manner of the connection according to Fig. 2, charge the condensers 33 and 33',

the negative potential of which is applied, with,

the inclusion of filters a and 35b and resistances 66, to the grid circuits of the detuning tubes 34 tem which enables the one of two tubes 34 to act potential of the circuit 2/3. The one tube then acts as capacity, whilst the other tube acts as inductance, one of both tubes always being blocked.

There are also other methods possible for obtaining comparison between and the synchronization of two frequencies. For example, in accordance with Fig. 4, two frequency meters may circuit 2, 3 of the generator I (Fig. 1) to which be provided, each of which indicates the fre- 76 quency by a frequency-proportional direct current. In Fig. 4, for example, coil 39 and condenser 40 are brought into resonance with the medium frequency of 30, and two detectors 4I/42 impart to the point 43 a potential which corresponds to the potential of the point 44 only in the case of resonance, but is positive or negative in the case of advance or retardation. If the same connection is made in respect of the generator 3| and if the two frequency meters are connected one against the other, there may be controlled by means of a connecting resistance 45 a D. C. amplifier 68, which in its anode circuit reproduces correctly according to extent and direction any deviation between the two frequencies 30 and 3| and may be employed for de-tuning the control transmitter of the synchronization generator.

It is possible by one of the described methods to maintain a delay of not more than one image period a permanent state of synchronism between the output oscillation of the synchronization generator and the local lighting mains, although all mains show periodic fluctuations of the frequency amounting to plus or minus a few per cent with a periodicity of 10-15 seconds. It is still to explain how the synchronized sine oscillations of line and image change frequency are converted intoimpulses. This problem may likewise be solved by the use of pentodes, the two control grids of which receive phase-shifted oscillations and the anode currents of which then show .impulses according to the phase-shift.

In Fig. 1 the two impulse tubes are designated 46 and 41 in respect of image and line. The anode current of the last frequency reducer is at first again conducted through a filter system. This comprises a step-down transformer 48in the anode circuit, which excites a series resonance system 49/50 to perform resonance oscillations. A pure sine oscillation of image change frequency may then be derived at the condenser 50. This is conducted to the inner grid of the image impulse pentode 46. The outer grid receives an oscillation in opposite phase from the grid circuit of the tube 63 by way of a phase-shifting member I/52. By reason 'of the phase shift there is regulated the length of the impulse. It is capable of being tapped at the anode resistance 53, which is connected to an anode battery 54. The potential of 54 is so low that a potential limitation occurs. The line impulse tube 41 is connected in parallel to the same resistance 53. Its two control grids are excited by the grid and anode circuits of the reducer stage I oscillating to the basic line frequency, the desired phase shift being adjusted betweenthe transforming circuit55 and 56. From a critical anode potential 54 downwards the impulses of both groups then have exactly the same height in volts, i. e., the anode potential is fully modulated.

In the practical embodiment an apparatus of this nature operates in the line number 343=7 7 7 with altogether four reducing stages, or in the line number 405=5 9x9 also with four reducing stages. -If, however, it is desired to avoid the excessive frequency reductions quency of said generator, said means consisting of q a tube having two control grids, each of said grids being so connected as to be excited by one of said frequencies, the smoothed anode current impulses generated in said tube being used for varying the frequency of said oscillatory circuit.

2. In a frequency reducer comprising a thermionic tube oscillation generator, an oscillatory circuit excited by said tube and several frequency reducing stages, means for synchronizing the last of said stages with a separate alternating voltage, particularly the mains, by adjusting the frequency of said generator, said means consisting of a tube having two control grids, each of said grids being so connected as to be excited by one of said frequencies, the smoothed anode current impulses generated in said tube controlling an amplifier tube the anode current of which shunts gradually said oscillatory circuit by an impedance, preferably a condenser, for reducing its frequency.

3. In a frequency reducer comprising a thermionic tube oscillation generator, an oscillatory circuit excited by said tube and several frequency reducing stages, means for synchronizing the last of said stages with a separate alternating voltage, particularly the mains, by adjusting the frequency of said generator, said means consisting of two tubes each having two control grids, each of said grids being so connected as to be excited by one of said frequencies, the phases of the excitation of both tubes being opposite to each other, the means to adjust the frequency of said generator consisting of a second pair of tubes the grids of which are connected to the output of said two tubes and the anode paths of which shunt the oscillatory circuit of said generator, the one of said pair of tubes acting as self-induction, the other one as capacity.

4. In a frequency reducer comprising a thermionic tube oscillation generator, an oscillatory circuit excited by said tube and several frequency reducing stages, means for synchronizing the last of said stages with a separate alternating voltage, particularly the mains, by adjusting the frequency of said generator, said means consisting of two series resonant circuits the one being connected to said last stage, the other one to said voltage, a rectifying detector in parallel to each of the coils andthe condensers of said resonant circuits, the middle points of both series of detectors being connected by a resistance, and means to utilize the direct current potential obtained on this resistance for adjusting the highest frequency of said cascade.

KURT SCI-ILESINGER. 

